In a drilling process using a fiber-reinforced composite material such as an FRP (fiber-reinforced plastic), especially, a CFRP (carbon fiber reinforced plastic) as a target member, inner fibers are hardly cut off. Thus, there has been a problem that the fibers become tangled to cause fluff on a peripheral wall of a hole, or laminated fiber layers are fell off to cause delamination on a peripheral wall of a hole. Further, large amounts of fibers are contained in chips generated in a drilling process for a fiber-reinforced composite material, and if the fibers are dispersed, the work environment is deteriorated. Thus, there is a need of reduction in the amount of chips generated during the drilling process.
In order to address such a problem and to respond to the demand, there has been disclosed a drilling tool (see FIGS. 1-3 in Japanese Patent Application Laid-Open Publication No. JP H2-237707) including a tool body 10 that rotates about an axis center O, a hole 10a that is open in a tip end surface of the tool body 10, a chip discharging groove 12 that is formed on an outer circumference of the tool body 10 while being communicated with the hole 10a, and a tip 13 that is fixed at a tip-end ridge line portion of the chip discharging groove 12. In the technique disclosed in JP H2-237707, a target member is not cut around the axis center O of the tool body 10. Thus, the target member inside the hole 10a is hollowed by a cutting blade 16 of the tip 13, and remains inside the hole 10a. In addition, only a part of the target member that is cut into by the cutting blade 16 becomes chips, and thus the amount of the chips generated can be reduced.